Source study of M w 5.4 April 4, 2011 India–Nepal border earthquake and scenario events in the Kumaon–Garhwal Region

Abstract

In the present work, ground motion is estimated from future scenario earthquakes at different sites in Uttarakhand Himalayas in India using empirical Green’s function (EGF) technique. The recorded ground motion from April 4, 2011, M w 5.4 earthquake is taken as a basic element. The ground motion is estimated at 24 sites, where the element earthquake was recorded. It is observed from synthesized time histories that sites located near the epicenter may expect accelerations in excess of 1 g. In the present analysis, Dharchula can expect ground accelerations in excess of 1 g. For M w 7.0, the expected peak values of acceleration (A max) and velocity (V max) on horizontal components at different sites range between 11 and 912 gal and 5 and 52 cm/s, respectively. The corresponding values for the Z component range between 8 and 228 gal, and 3 and 14 cm/s, respectively. Similarly, for M w 7.5, the expected A max and V max on horizontal components at different sites range between 25 and 1281 gal and 25 and 102 cm/s, respectively. The corresponding values for the Z component range between 14 to 474 gal, and 15 to 70 cm/s, respectively. The site amplification functions are estimated using the horizontal-to-vertical spectral ratio procedure. Zone IV (on a scale of II to V according to the seismic zonation map for India) response spectrum for 5 % damping is deficient for M w 7.0, while zone V response spectrum is exceeded at several frequencies for same magnitude. For M w 7.5, zone IV response spectrum is conservative (except at some frequencies), while zone V response spectrum is exceeded at many sites. The estimated PGA values can be incorporated in marking the weak areas in the central Himalaya, thereby assisting the designing and construction of new structures.